1. Field of the Invention
This invention relates to apparatus for quantifying visual function defects. The invention also relates to a testing element for use in quantifying visual function defects. The apparatus and testing element are particularly applicable to the detection of colour vision defects.
2. Description of the Prior Art
There are a number of known methods of testing eye defects.
For example, in testing colour blindness the FM (Farnsworth-Munsell) 100 Hue test is of considerable value in the detection and diagnosis of acquired dyschromatopsias and in providing a means of classification of congenital colour vision deficiences. The test is described in detail in the following articles: "The Farnsworth-Munsell 100 Hue Test and Dichotomous Tests for Color Vision" by D. Farnsworth in the Journal of the Optical Society of America, volume 33, No. 10, October 1953, pages 568 to 578; and "The Farnsworth-Munsell 100 Hue Test for the Examination of Color Discrimination", a manual by D. Farnsworth published in 1949 by the Munsell Color Company Inc.
In this test a plurality of coloured discs are arranged in a selected order by a subject being tested. The discrepancies between the selected order and the correct order can be analysed to provide a reliable diagnosis of the subject's colour vision defects.
Unfortunately the analysis is time consuming and for this reason the FM 100 Hue Test is unpopular in clinics.
A computerised testing apparatus has been devised and this is described in the following articles: "Recent Developments in Farnsworth's. Colour Vision Tests" by W. O. G. Taylor et al in the Transactions of the Ophthalmic Society UK, volume 96, 1976, pages 262 to 264; and in "Instrumentation for the Farnsworth-Munsell 100 Hue Test" by G. B. Donaldson in the Journal of the Optical Society of America, volume 67, No. 2, February 1977, pages. 248 and 249. These devices use differentially coded resistors which identify each particular coloured disc.
The computerised apparatus. considerably reduces the time involved in analysing the test results, but unfortunately is extremely expensive.